Allosteric modulation of 5-HT(1A) receptors by zinc: Binding studies.
5-HT(1A) receptors were studied via [(3)H]WAY-100635 and [(3)H]8-OH-DPAT binding to rat brain cortical membranes. We characterized the effect of zinc (Zn(2+)) on the binding properties of the 5-HT(1A) receptor. The allosteric ternary complex model was applied to determine the dissociation constant (K(A)) of Zn(2+) and their cooperativity factors (alpha) affecting the dissociation constants (K(D), K(i)) of [(3)H]WAY-100635, [(3)H]8-OH-DPAT, and serotonin (5-HT), the endogenous neurotransmitter. Zn(2+) (5microM-1mM) inhibited the binding of agonist/antagonist to 5-HT1A receptors, mostly by decreasing both the ligands' affinity and the maximal number of sites. In [(35)S]GTPgammaS binding assays Zn(2+) behaved as insourmountable antagonist of 5-HT1A receptors, in agreement with radioligand binding assays. The residues involved in the formation of the inhibitory binding site on the 5-HT1A receptor were assessed by using N-ethyl-maleimide (NEM) or diethylpyrocarbonate (DEPC) which modify preferentially cysteine and histidine residues, respectively. Exposure to both agents did not block the negative allosteric effects of Zn(2+) on agonist and antagonist binding. Our findings represent the first quantitative analysis of allosteric binding interactions for 5-HT(1A) receptors. The physiological significance of Zn(2+) modulation of 5-HT(1A) receptors is unclear, but the colocalization of 5-HT(1A) receptors and Zn(2+) in the nervous system (e.g. in the hippocampus and cerebral cortex) suggests that Zn(2+) released at nerve terminals may modulate signals generated by the 5-HT(1A) receptors in vivo. Finally, these findings suggest that synaptic Zn(2+) may be a factor influencing the effectiveness of therapies that rely on 5-HT(1A) receptor activity.
Barrondo
Sergio
S
Departamento de Farmacología, Facultad de Farmacia, Universidad del País Vasco/EHU, Paseo de la Universidad 7, 01006-Vitoria-Gasteiz, Alava, Spain.
Sallés
Joan
J
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000494:pharmacology; D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D001667:Binding, Competitive / Q000187:drug effects*; D002462:Cell Membrane / Q000187:drug effects; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects; D002712:Chlorides / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D020128:Inhibitory Concentration 50; D008297:Male; D009716:Numerical Analysis, Computer-Assisted; D010879:Piperazines / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D011725:Pyridines / Q000494:pharmacology; D011869:Radioligand Assay / Q000379:methods; D051381:Rats; D044282:Receptor, Serotonin, 5-HT1A / Q000187:drug effects / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D014316:Tritium / Q000494:pharmacology; D017967:Zinc Compounds / Q000494:pharmacology*
D002712:Chlorides; D010879:Piperazines; D011725:Pyridines; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D017967:Zinc Compounds; D014316:Tritium; D044282:Receptor, Serotonin, 5-HT1A; D012701:Serotonin; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C090413:N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; C016837:zinc chloride